Measurements of the degree of rotation of plane polarised light by a sample as a function of wavelength and concentration are important in inter alia the field of biology and biological research. Such measurements of optical activity have formed the basis of optical polarimetry utilised to assess chirality and optical isomerism for over a century and remain important as (in most other respects) optical isomers have identical properties which in general makes them difficult to distinguish or separate. For example, such measurements enable a biologically active optical isomer to be distinguished from its complementary optical isomer which may be biologically inactive.
Techniques relating to optical activity have been extended to include inter alia circular dichroism (CD) spectroscopy in which the behaviour of circularly polarised light is analysed at different wavelengths. When such wavelengths are in the UV region, important data relating (for example) to the structure and folding of proteins can be deduced. This is because the different tertiary structures adopted by protein molecules (especially alpha helical and beta pleated sheets) tend to be asymmetrical and have intrinsic optical properties which can be differentiated in terms of their optical activity. Whilst such data is very useful, its analysis is subject to some ambiguity.